Many women don’t know whether they have dense breast tissue—even though it can have an impact on their cancer risk and cancer screenings. Breast density has nothing to do with the size or firmness of your breasts. Instead, it describes the relative amount of three types of tissue—glandular, connective, and fat—in your breasts. Dense breasts have more glandular and connective tissue and less fat than non-dense breasts, which are mostly fat tissue.
You can’t tell if your breasts are dense by feeling or looking at them. Only a mammogram can detect dense breasts.
An estimated 43 percent of women ages 40 to 74 who have mammograms have dense breasts. Most women’s breasts begin to lose density around age 50, primarily during menopause. Some factors associated with higher density include a low body mass index, never having had children, and use of menopausal hormone therapy. Genetics may also play a role in breast density.
Breast density and cancer risk
Evidence suggests that women with dense breasts are at a higher risk of being diagnosed with breast cancer—but not dying from it—than those with less dense areas of breast tissue. The risk increases as density increases. However, the extent of risk isn’t established, and having dense tissue usually isn’t considered a stand-alone risk factor. In other words, doctors take breast density into account when you have other factors that put you at high risk for breast cancer.
Breast density can also affect mammogram accuracy. Dense breasts make it harder for radiologists to evaluate and detect an abnormality on a mammogram. The dense tissue can mistakenly appear as tumors or masses on a mammogram, making it difficult to distinguish one from the other. Dense tissue can also obscure a radiologist’s view and hide tumors.
Women with dense breasts have a higher rate of false-positive mammograms (a suggestion of an abnormality that could be cancer when none exists) than women who don’t have dense breasts. Moreover, mammogram interpretations by different radiologists aren’t always consistent, so assessments of breast density can vary from one mammogram to another.
Breast Density Classifications
Breast density is often grouped into four classifications (A, B, C, and D) using the Breast Imaging Reporting and Data System, or BI-RADS.
Your doctor might suggest you undergo a type of three-dimensional (3-D) mammography called digital breast tomosynthesis, which modestly increases the likelihood of accurately detecting abnormalities and decreases false positives. Medical societies like the American Cancer Society, however, haven’t wholeheartedly endorsed 3-D mammograms, citing a lack of evidence comparing them to standard mammograms. 3-D mammograms aren’t widely available, may not be covered by insurance, and expose women to additional radiation.
Supplemental screening options
Some doctors recommend routine mammograms supplemented with a breast ultrasound for women with dense breasts. It’s not clear, though, whether an ultrasound is beneficial, mainly because of the increased rate of false positives it generates. There’s no solid evidence that women with dense breasts benefit from an ultrasound or other modes of screening such as magnetic resonance imaging (MRI) unless they’re at high risk for breast cancer because of family history, a gene mutation (BRCA1 or BRCA2), or another factor.
A study published in JAMA Internal Medicine in March 2019 concluded that a mammogram with ultrasound was no more likely to detect breast cancer than mammography alone, and therefore, the benefits of a screening ultrasound in women of average risk don’t outweigh its potential harms, such as a breast biopsy. Follow-up procedures put women at risk for complications, pain, anxiety, and stress.
Another study in JAMA Internal Medicine, published in July 2019, suggests that women with dense breasts and a high risk for advanced cancer be counseled about supplemental imaging but advised against additional screening based on density alone.
Keeping abreast of density
Currently, 36 states require that women be notified if they have dense breasts when they receive their mammography results. Women who live in states with breast density reporting laws are more likely to have discussed the need for additional screening with their doctors, according to a survey of 1,500 women published in February 2019 in the Journal of the American College of Radiology.
In March 2019, the FDA proposed a rule that would require all mammography reports to notify women of their breast density. The report would also make women aware of their risks and supplemental screening options.
There is no medical consensus for how to follow up after a mammogram shows dense breasts. That’s why it’s important to talk with your doctor about breast density, your risk of developing breast cancer, and the possible use of 3-D mammograms, MRI, or ultrasound to make a truly informed decision.
This article first appeared in UC Berkeley Health After 50.
Published October 28, 2019